A centralized alarm monitoring system is an efficient way to handle alarm reporting from multiple remote customer sites. Typically, an alarm control panel at a customer site includes an automatic dialer that is pre-programmed to call a central monitoring station upon detection of an alarm event. When the call is completed through the public switched telephone network to the central monitoring station, the alarm control panel sends an alarm message to the central station for processing and response. One problem is that the central station may not be accessible. This may be due to telephone network congestion, a network fault, or a fault at the central station itself.
One approach to the problem of inaccessibility of the central station is to periodically redial the access number until the call can be completed. This approach has the difficulty that if there is a network fault or a fault in the central station, the call cannot be completed and thus the alarm message cannot be delivered.
Another approach is to program the dialer with a secondary access number for reaching the central station. This approach is useful for the case where the primary access number is busy. However, this approach suffers from the same difficulty as the first approach in that the call cannot be completed if there is a network fault or a fault in the central station. Another difficulty is that many customer sites may have dialers that can only be programmed to dial a single access number.